[fransje26]

> I don’t see why a li-ion battery pack wouldn’t be usable for 15 years.

For 2 reasons, primarily. First, Toyota chose nickel-cadmium batteries because of their higher charge-cycle life, at the cost of a much lower energy density (about half that of li-ion). Secondly, they designed their system so that the discharge rate and the discharge level of their battery pack stayed low, thereby maximizing the lifetime of their battery pack, at the cost, once more, of extra weight.

So those two aspects combined mean that you can expect a much longer real-life usage of your battery pack before reduced performance becomes an issue.

I fully agree that a battery pack replacement after 15 years could be considered reasonable (as long as the build quality of the rest of the car warrants it, which is not a given nowadays). But if the mean-time between replacement is around 5 years, then it becomes unreasonable.